Identification of odorous compounds from nine fermentor-cultivated Streptomyces strains

Profiling and characterization of odorous volatile compounds from the industrial fermentation of erythromycin

Complaints caused by odors from the fermentation production of pharmaceuticals are common in China. The elimination of odor remains a challenge for the pharmaceutical industry to meet the increasingly strict environment regulations. Erythromycin is a representative antibiotic produced by microbial fermentation. The fermentation exhaust gas of erythromycin fermentation has an unpleasant odor, but the composition of the key odorants has not been identified. The major odorants from the fermentation production of erythromycin API were analyzed by electronic nose, olfactory measurements, gas chromatography-coupled ion mobility spectrometry (GC-IMS) and gas chromatography-mass spectrometry (GC-MS) analysis. Two compounds, 2-methylisoborneol (2-MIB) and geosmin, were identified as the major odorants of erythromycin fermentation. These had not been detected before using only GC-MS analysis of exhaust gas. Aldehydes, including hexanal, octanal, decanal, and benzaldehyde, also contribute to the odor. The composition analysis of odorants using the fermentation broth headspace was more efficient and reliable, considering the significant dilution effect of exhaust gas. The concentration of 2-MIB and geosmin in the fermentation broth greatly exceeded their odor thresholds. The production of major odorants started in the early fermentation stage and became significant in the middle stage (30-70 h). Due to the extremely low odor thresholds of 2-MIB and geosmin, advanced purification may require deodorization of erythromycin fermentation exhaust gas.

Functional diversity among sensory receptors in a Drosophila olfactory circuit

The ability of an animal to detect, discriminate, and respond to odors depends on the function of its olfactory receptor neurons (ORNs), which in turn depends ultimately on odorant receptors. To understand the diverse mechanisms used by an animal in olfactory coding and computation, it is essential to understand the functional diversity of its odor receptors. The larval olfactory system of Drosophila melanogaster contains 21 ORNs and a comparable number of odorant receptors whose properties have been examined in only a limited way. We systematically screened them with a panel of ∼500 odorants, yielding >10,000 receptor-odorant combinations. We identify for each of 19 receptors an odorant that excites it strongly. The responses elicited by each of these odorants are analyzed in detail. The odorants elicited little cross-activation of other receptors at the test concentration; thus, low concentrations of many of these odorants in nature may be signaled by a single ORN. The receptors differed dramatically in sensitivity to their cognate odorants. The responses showed diverse temporal dynamics, with some odorants eliciting supersustained responses. An intriguing question in the field concerns the roles of different ORNs and receptors in driving behavior. We found that the cognate odorants elicited behavioral responses that varied across a broad range. Some odorants elicited strong physiological responses but weak behavioral responses or weak physiological responses but strong behavioral responses.

Characterization of geosmin as source of earthy odor in different aroma type Chinese liquors

Earthy odor is one of the most frequent and serious causes for the aroma deterioration in Chinese liquor, which causes a dirty and dusty impression. The odor in Chinese liquor is similar to that of rice husk, one kind of auxiliary material widely used as a filler in the distillation process. So it is experientially hypothesized that such odor may derive from rice husk. In this paper, the gas chromatography-olfactometry (GC-O) technique and gas chromatography-mass spectrometry (GC-MS) were used to discover and identify the characteristic odoriferous zone of Chinese liquor marked by earthy odor. Geosmin was found to be responsible for this odor. The levels of the compound in ten bottled liquors and thirty liquors aging for different years belonging to four different aroma types were determined by the optimized headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) method. Quantitative analysis of bottled liquor revealed the presence of geosmin in all aroma type liquors with concentrations ranging from 1.10 μg/L to 9.90 μg/L, except for strong-aroma type liquor. Meanwhile in the aged liquors belonging to the same aroma type, geosmin was detected with significant concentrations and high odor activity values (OAVs) during different years of aging. However, geosmin was not detected in steamed rice husk nor in nonsteamed rice husk, which suggests that rice husk is not the origin of earthy odor in Chinese liquor, and there may be another origin of it during the brewing process.